1. Field of the Invention
The present invention relates to a contact-pressure adjusting method and a contact-pressure adjusting system for a liquid application machine.
2. Description of the Related Art
In a printing press, after the start of printing, the temperature inside the printing press gradually increases with the operating time. Since each component of the printing press thermally expands due to the increase in temperature, the contact pressure (a nip pressure or a printing pressure) of every part of the printing press changes from a value that is set at the start of printing. For the purpose of compensating for the change, the printing press has the following structures. Specifically, it is possible to adjust the contact pressure between a form roller, which applies ink to a plate surface, and the plate surface, while the printing press is in operation. In addition, it is also possible to adjust the contact pressure between the plate surface and an impression cylinder, as well as the contact pressure between the plate surface and a blanket cylinder. Particularly in a relief printing, such a change in contact pressure causes printing troubles, such as the darkening of colors and the thickening of lines, near the raised portions. For this reason, the operator has to frequently adjust the contact pressure while checking printing products all the time. In addition, such an increase in temperature varies depending on various factors, such as printing patterns, printing systems, the number of colors to be used, and printing materials to be used. Minute changes in contact pressure due to these factors affect largely on printing products. Accordingly, for the purpose of compensating for the change in contact pressure, a printing press is provided with a contact-pressure adjusting system which adjusts the contact pressure during operation of the printing press. Examples of such a contact-pressure adjusting system are disclosed in Japanese Utility Model Application Laid-open Publication Nos. Hei 1-171642, Hei 3-124838, Hei 4-128835, and Sho 63-141732, as well as Japanese Unexamined Patent Application Publication No. Sho 63-264354.
However, in the contact-pressure adjusting systems disclosed in the above publications, it is necessary for the operator to manually adjust a contact pressure (a nip pressure or a printing pressure) very frequently. Accordingly, a heavy burden is imposed on the operator. In addition, since a contact pressure is adjusted in accordance with the operator's gut feeling based on his or her experience, the quality of printing products varies depending on the operators. Moreover, the changes, with the operation time, in contact pressures bring about changes of the quality of printing products.